Neural connections identified with PHA-L anterograde and HRP retrograde tract-tracing techniques.

This paper describes a method of identifying specific input and output elements of a two-neuron projection pathway. Phaseolus vulgaris leucoagglutinin (PHA-L) anterograde tract-tracing was used in combination with the retrograde transport of horseradish peroxidase (HRP) to demonstrate connections between small groups of neurons in the brainstem auditory system. Specifically, the projection from cochlear nucleus to olivary neurons that project to the cochlea were demonstrated. The first neuron in this pathway (the cochlear nucleus neuron) was anterogradely labelled with PHA-L and could be traced via labelled axons and terminals to the second neuron (the olivocochlear neuron) whose soma was labelled with HRP after cochlear injection.